The present invention relates to liquid crystal display devices and, more particularly, to optical filters in fluorescent liquid crystal display devices.
R. D. Larrabee has already proposed to add a fluorescent material to a liquid crystal material and to vary fluorescent intensity of the fluorescent material by altering the electric field across the liquid crystal material (RCA Review, Vol 34, P 329, 1973). However, his paper states that he failed to find liquid crystal materials which do not absorb ultraviolet light at room temperature. This appears attributable to the fact that, when causing a fluorescent material in a liquid crystal material to absorb a varying amount of light in accordance with the orientation of the liquid crystal, to vary the flourescence intensity with the light absorption, the exciting light is absorbed by the liquid crystal layer without effectively exciting the flourescent material.
The present inventors have proposed an improved fluorescent liquid crystal display as U.S. patent application Ser. No. 935,246 filed on Aug. 21, 1978 wherein light scattering phenomena takes place in the fluorescent liquid crystal display in response to excitation of an electric field, heat or the like and the flourescence emitted from the fluorescent material is effectively taken out of the flourescent material contained within a liquid crystal display. The corresponding German Patent Application P No. 28 37 257.8 was filed with the German Patent Office on Aug. 25, 1978.
The disclosure of R. D. Larrabee and the U.S. patent application Ser. No. 935,246 are incorporated herein by reference.
It is required in the above-mentioned fluorescent liquid crystal display that display contrast of the liquid crystal display be enhanced for excellent visibility. The present invention can be applied to the fluorescent liquid crystal display of R. D. Larrabee and the U.S. patent application Ser. No. 935,246.